Analyte concentration detection devices and methods

ABSTRACT

Arrangements for the detection of the presence and/or concentration of an analyte in a sample of bodily fluid include diffuse transmission, diffuse reflection and edge or waveguide illumination arrangements. A vertical flow assay arrangement and/or technique is also disclosed, and includes a detection component that can be in the form of an array of optical detection elements. A number of assay pad constructions are described which may include at least one or more of the following components: a prefilter component, a reflective component, a membrane component, a reagent component, a mesh component, and a component to prevent lateral spreading.

The present application is a continuation of U.S. patent applicationSer. No. 10/394,230 filed Mar. 24, 2003, the content of which isincorporated herein by reference, in its entirety.

FIELD OF THE INVENTION

The present invention is directed to techniques and devices fordetection of the presence and/or concentration of an analyte.

BACKGROUND OF THE INVENTION

A survey of the prior art reveals that numerous techniques and devicesfor performing an assay to determine the presence and/or concentrate ofan analyte have been developed.

SUMMARY OF THE INVENTION

According to the present invention, the state of the art has beenadvanced through the provision of devices and techniques such as thosedescribed further herein, for accurately, efficiently, and economicallydetermining the presence and/or concentration of an analyte. Accordingto the present invention, the state of the art has been advanced,especially, but not exclusively, within the context of personal glucosemonitoring devices and techniques.

According to one aspect, the present invention provides a device formonitoring the concentration of an analyte present in bodily fluid, thedevice comprising a detector, the detector comprising a sensor, thesensor comprising a CMOS sensor, a CCD sensor, or a photodiode.

According to a further aspect, the present invention provides a devicefor conducting an assay to determine the concentration of an analyte ina sample of bodily fluid, the device comprising: a sample collectionchannel having a bottom with at least one opening; an assay pad incommunication with the at least one opening of the channel, the assaypad comprising a reagent adapted to produce a chemical reaction whenexposed to the analyte, the chemical reaction producing a color changein the assay pad; and a linear array of CMOS optical detectors disposedrelative to the assay pad so as to detect the color change.

According to a further aspect, the present invention provides an assaypad construction comprising: a first component comprising a constituentto separate red blood cells from plasma and further comprising a diffusereflective material constituent; a second component comprising achemical reagent; and a third component comprising apolyamide-containing mesh.

According to yet another aspect, the present invention provides an assaypad comprising: a first component comprising a diffuse reflectivematerial; a second component comprising a hydrophilic material; a thirdcomponent comprising a reagent; and a fourth component comprising a meshor a membrane.

According to another aspect, the present invention provides a method ofperforming an assay to determine the concentration of an analyte in asample of bodily fluid, the method comprising: (i) providing a samplecollection channel having a first volume; (ii) introducing a sample ofbodily fluid into the channel, the sample introduced into the channelhaving a second volume which is less than the first volume; (iii)vertically conveying the sample from the channel onto an assay pad; (iv)reacting the analyte in the sample with a chemical reagent in the assaypad thereby producing a color change in the assay pad; and (v) detectingthe color change with a linear array of CMOS sensors by detecting thecolor change with each individual CMOS sensor in the array which isincident upon the area of color change in the assay pad.

According to still another aspect, the present invention provides amethod of determining an estimated volume of a sample of bodily fluidbeing subjected to an assay, the method comprising: (i) providing anelongated sample collection channel having a volume directlyproportional to its length; (ii) introducing a sample of bodily fluidinto the channel; (iii) vertically conveying the sample from the channelonto an assay pad; (iv) reacting the analyte in the sample with achemical reagent in the assay pad thereby producing a color change inthe assay pad; (v) disposing a linear array of CMOS sensors incident tothe assay pad for detecting the color change, the length of the CMOSarray being commensurate with the length of the collection channel; (vi)detecting the color change with each individual CMOS sensor in the arraywhich is incident upon the area of color change in the assay pad; and(v) calculating the estimated volume of the sample in the collectionchamber based upon the number of sensors in the linear array whichdetect the change in color.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of an analyte detection arrangementaccording to the present invention.

FIG. 2 is a schematic illustration of an analyte detection arrangementaccording to another aspect of the present invention.

FIG. 3 is a schematic illustration of an analyte detection arrangementaccording to a further aspect of the present invention.

FIG. 4 is a schematic illustration of an analyte detection arrangementaccording to another aspect of the present invention.

FIG. 5 is a schematic illustration of an analyte detection arrangementaccording to a further aspect of the present invention.

FIG. 6 is a schematic illustration of an analyte detection according toanother aspect of the present invention.

FIG. 7 is a schematic illustration of an analyte detection arrangementaccording to a further aspect of the present invention.

FIG. 8A is a schematic illustration of an assay arrangement andtechnique according to the present invention.

FIG. 8B is a cross-section of FIG. 8A taken along line 8B-8B.

FIG. 9 is picture of an exemplary reaction spot according to the presentinvention.

FIG. 10 is a scan along the dashed line of FIG. 9.

FIG. 11 is a schematic illustration of a layered test strip constructedaccording to the present invention.

FIG. 12 is a schematic illustration of another layered test stripconstruction according to the present invention.

FIG. 13 is a picture of a mesh wherein at least a portion thereofincludes retained reagent.

FIG. 14 is a schematic illustration of a further layered test stripconstruction according to the present invention.

FIG. 15 is a schematic illustration of yet another layered test stripconstruction according to the present invention.

FIG. 16 is a schematic illustration of a further layered test stripconstruction according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Exemplary arrangements for the detection and measurement of the presenceand/or concentration of an analyte, such as glucose, will now bedescribed by reference to the drawing figures.

FIG. 1 is one such arrangement 100 for the optical detection of thepresence and/or concentration of an analyte such as glucose. Thearrangement 100 can generally be described as a diffuse transmissionarrangement.

According to this embodiment of the present invention, the substance tobe analyzed is transported via a conduit 12. When the substance to beanalyzed comprises a sample of whole blood, interstitial fluid, ormixture thereof, the conduit 12 can be in the form of a hollow member orneedle. The needle can be of a very narrow gage, or a so-calledmicroneedle. Such a needle typically having a size on the order of40-100 micrometers.

The microneedle may also act as a skin penetration member as well as aconduit. Alternatively, the skin penetration member may be in the formof a solid lancet (not shown), which acts to produce a sample of bodilyfluid which is then transported via conduit, e.g.—12.

The substance to be analyzed is transported via the conduit 12 to achamber 14. The chamber may have any suitable form. According to oneembodiment, the chamber 14 is formed by a lower member 16 and an uppermember 18. These members 16, 18 can be constructed to allow light to betransmitted therethrough.

An assay pad 20 is provided within the chamber 14. The pad 20 receivesthe substance to be analyzed. The pad 20 is provided with a substancethat reacts with the analyte. The results of this reaction is detectableand the data generated through detection is used to determine thepresence and/or concentration of the analyte. According to theprinciples of the present invention, the pad 20 is provided with aconstruction to achieve this objective, and others. A discussion of thespecifics of the pad 20 will be deferred.

A light source 22 can be provided so as to produce light that isincident upon a first side of the pad 20. Any suitable light source isenvisioned. According to a preferred embodiment, the light sourcecomprises a light emitting diode (LED). The LED or light source 22 canprovide incident light of any suitable wavelength. Wavelengths on theorder of 500-700 nm are suitable. For example, incident light with awavelength on the order of 670 nm may be transmitted from light source22. At approximately 670 nm, absorption of the incident light byhemoglobin tends to be reduced.

An optical detector 24 is positioned so as to receive light transmittedthrough a second side of the pad 20, the second side being opposite thefirst side. The optical detector can be a digital imaging device, suchas a complementary metal oxide semiconductor (CMOS) device, a chargecouple device (CCD), or any photodiode. The imaging device may compriseand array of individual detectors.

According to the present invention, the implementation of digitalimaging devices permits the analysis of samples that are not of uniformvolume. This is accomplished at least in part by the ability ofindividual detectors to take readings, which are then averaged orcombined to generate an overall reading. The larger the sample, thelarger the “spot” formed on the pad 20, and the more individualdetectors pick up a reading of the reaction occurring in the pad 20.Thus, unlike assays performed by conventional personal glucosemonitoring devices and the like, the assay of the present invention isnot dependent upon the volume of the sample being analyzed. When anassay is incorporated into a monitoring device wherein the monitoring isperformed in an automated fashion, the user is often unable to determineif a sample of body fluid of a particular volume has been obtained. Inconventional assays, the accuracy of the assay is directly linked to aspecific volume of sample undergoing analysis (e.g.—“microtitration”).The present invention breaks this dependence, thereby providing robustand reliable devices, such as personal glucose monitoring devices, thatcan function effectively over a range of potential sample volumes. Otherdetails of the detector 24, and associated components, will be deferredto later text.

The arrangement 100 may be incorporated into a larger overall device.According to one embodiment, the arrangement 100 is incorporated into apersonal glucose-monitoring device. According to one alternative, thedevice is ambulatory. The arrangement 100 can be incorporated intodevices, such as the ones described in U.S. Patent Publication No. US2002/0087056 or US 2003/0153900, both of which are incorporated hereinby reference in their entirety.

In the following description of alternative arrangements, those elementsthat correspond to features already described in previous arrangement(s)have been designated with the same reference numbers.

An alternative arrangement 200 is depicted in FIG. 2. The arrangement200 can generally be described as a diffuse reflection arrangement.

While arrangement 200 is similar to the previously described arrangement100, the light source 22 is provided such that it transmits light whichis incident upon a first side of the assay pad 20. At least a portion ofthis incident light is reflected off of the first side. This reflectedlight can then be collected by the optical detector 24, which isdisposed on the same side as the light source 22, relative to the testpad 20. Preferably, the light source 22 and the optical detector 24 aredisposed, relative to the reaction chamber, on a side which is oppositefrom the side of the reaction chamber into which the conduit 12introduces the substance to be analyzed. This orientation is shown inFIG. 2.

In order to improve reflection of the incident light from the test pad,the test pad 20 may be provided with a blocking layer 21. Such a layercan be formed of any suitable material, such as zirconium oxide ortitanium oxide.

Since only one side of the test pad is read by the detector, the readingtaken by the detector 24 is insensitive to the contents of the chamber14 since the contents of the chamber 14 are not in direct communicationwith the side of the test pad 20 being read.

Another alternative arrangement constructed according to the principlesof the present invention is illustrated in FIG. 3. The arrangement 300can generally be described as an edge or waveguide illuminationarrangement.

According to this aspect of the present invention, a light source 22 isarranged such that a diverging light beam strikes an edge of atransparent waveguide member 32, and couples the transmitted lightinside the waveguide, as illustrated by the broken lines contained inFIG. 3.

When the angle of incident light is greater than a critical angle ofincidence, “θC”, losses of incident light due to reflection areminimized. This critical angle can be expressed as θ_(C)=sin⁻¹(n₂/n₁),where θ_(c) is the angle of incidence that will cause incident light tobecome trapped in the waveguide, and n₂ and n₁ are the indices ofrefraction for a first material and a second material that define aboundary across which the light is attempting to travel (e.g.—air andtest strip material).

In order to further minimize such losses, the coupling edge of thewaveguide may be treated with an anti reflective coating or anindex-matching medium. For example, one or more thin layers of siliconoxide may be applied to the coupling edge. A thickness of approximately200 nm is an exemplary thickness.

Light trapped inside the waveguide propagates by total internalreflection (TIR) until it encounters the assay pad 20 which is affixedto or in communication with a surface of the waveguide, as illustratedin FIG. 3. The assay pad 20 is provided with a surface in communicationwith the reflected light inside the waveguide, which is lightscattering. Light impinging on this surface 34 of a test pad 20 isscattered at all angles. As illustrated by the dotted lines in FIG. 3,some of the light is scattered at a large angle relative to the normalof surface 34. This light is also trapped inside the waveguide. However,some of the light is scattered at a relatively small angle compared tothe normal of surface 34, as illustrated by the solid double arrow linesof FIG. 3, and is consequently transmitted outside of the waveguide andreceived by the detector 24.

Another arrangement 400 of the type described above, is also illustratedin FIG. 4. As illustrated in FIGS. 3 and 4, arrangements of this type(300, 400) are such that light provided by the light source 22 isincident upon the waveguide at a relatively small angle to the surfacethereof, a larger amount of this incident light is transmitted throughthe waveguide, when compared with arrangements wherein the incidentlight is provided at a relatively steep angle to the incident surface.Thus, when the light source is an LED-type source, less power isrequired in order to provide the necessary amount of incident light toperform the assay, and power consumption can be minimized.

The light source 22 can be closely aligned with the edge of thewaveguide 32, and thus may provide for a compact configuration. Inaddition, the detector element 24 can be positioned in close proximityto the waveguide 32, assay pad 20 and light source 22 (FIG. 4), therebyenabling it to be more protected from stray light sources.

In certain instances, it may be desirable to provide an arrangement 500as depicted in FIG. 5. In this arrangement 500, an imaging lens 52 isprovided and disposed such that it captures and focuses light reflectedfrom the assay pad 20 toward the optical detector 24. The lens 52 maycomprise a refractive or defractive element (Fresnel lens).

In FIG. 5, the lens 52 is utilized in connection with an edgeillumination-type arrangement.

Although the lens 52 is illustrated as being disposed at some distancefrom the waveguide 32 which forms the upper portion of the reactionchamber 14, the lens member may also be integrated into either thesurface of the detector 24, or into the upper member (e.g.—18, FIG. 1)or waveguide 32.

FIG. 6 depicts an alternative arrangement 600 which comprises a diffusereflection type arrangement which incorporates an imaging lens member52, as described above.

Another arrangement 700 is depicted in FIG. 7. The arrangement 700includes an edge-illumination type arrangement including waveguide 32.An imaging lens 54 is also included. In this arrangement, the imaginglens is integrated into either the waveguide 32 or the detector 24.

FIGS. 8 a and 8 b illustrate in further detail certain aspects of anadditional embodiment of the present invention. FIGS. 8 a and 8 billustrate and arrangement 80 which can be generally described as avertical-flow assay.

The arrangement 800 includes a channel member 82 having an open“bottom”, an assay pad 20 in communication with the open bottom ofchannel member 82, and an optical detector, preferably in the form of anarray 84 of digital imaging devices 85. According to one preferredaspect of the invention, lens elements 86 are incorporated into thearrangement. Although lens elements 86 are illustrated as being in theform of discrete individual lenses in close proximity to the individualdetector elements or pixels 85, it is within the scope of the presentinvention that alternative constructions are possible. For example, thelenses 86 could be spaced from the detectors 85, and/or a singleintegrated lens construction could be utilized instead of discretelenses 86.

As previously noted, arrangements of the type depicted in FIGS. 8 a and8 b permit the reliable and effective analysis of relatively smallamounts of substances, which is not dependent upon a particularrepeatable volume.

The channel member 82 is elongated. In other words, the substance beinganalyzed, such as a sample of body fluid is introduced at one end 81 ofthe channel member 82 and flows laterally or axially therethrough. Thesubstance being analyzed then permeates the test pad 20 disposedthereunder. While the open channel member 82 defines a particularvolume, it is not necessary to completely fill the channel member 82 inorder to conduct an accurate analysis. For example, as illustrated inFIG. 8A, a particular volume of substance to be tested may onlypartially fill channel member 82, for example, it may only fill channelmember 82 up to the point defined along line 83. When conducting ananalysis, the independent detector pixels 85 of the array 84 on theleft-hand side of line 83 are activated and will take a reading from theanalysis side of the test pad 20 once the analyte present in substanceunder analysis reacts with the chemicals contained in the test pad 20.Those individual detector elements of the array which are on theleft-hand side of line 83 will generate a signal which is indicative ofthe presence of this reaction. Those individual detector elements 85 ofarray 84 which are on the right hand side of line 83 will not generatesuch a reading. Thus, the readings or data generated by each individualdetector element 85 of the array 84 is taken and analyzed, such as byaveraging, to generate an overall reading of the presence and/orconcentration of a particular analyte contained in the substance underanalysis.

Moreover, since the volume of the channel member 82 is known, and thelength of the detector element contained in the array 84, as well as anycorrection due to the presence of lens elements 86 are known, the volumeof the sample under analysis can be estimated based upon the number ofpixels which detect the reaction between the analyte and the chemicalreagents contained in test pad 20. An exemplary, non-limiting embodimentwill now be described to further illustrate the principles of thepresent invention.

The time between the readings taken by the detectors 85 of the array 84can also be monitored by the electronics of the arrangement. Thespecific means of implementing this monitoring being well within theskill of those in the art. Thus, the arrangement of the presentinvention can also analyze the kinetics of the reaction between theanalyte and the chemical reagents, thereby offering the possibly toprovide additional useful information that can be used to provide aninsightful analysis of the sample.

An arrangement 80 of the type depicted in FIGS. 8 a through 8 b canadvantageously be utilized to analyze very small volumes of a substanceto be tested. For example, the arrangement can be utilized to assay1-500 nanoliter (nL) volumes. The substance to be tested may includewhole blood, interstitial fluid, or combinations thereof.

Assuming a nominal 250 nanoliter maximum volume, a sample of body fluidis introduced along direction B₁ from the right hand side 81 of channelnumber 82 through any suitable means, such as conduit 14 (see,e.g.—FIGS. 1 through 2). The sample is extended laterally into theelongated channel member 82. The sample is extended over a relativelylong length, which can be on the order of a few millimeters. Accordingto one specific example, the channel is approximately 250 micrometers(width)×140 micrometers (height)×7,000 micrometers (length). The sampleof body fluid then flows vertically along direction B₂ through the openbottom portion of channel 82 and into the assay pad 20. A color changein the assay pad 20 may be produced by a chemical reaction triggered bythe presence of a specific analyte contained in the sample of bodyfluid, such as glucose. This color change can be detected on theopposite of the assay pad from which the sample of body fluid isintroduced. This color change is detected by a suitable detectiondevice, such as the optical detector array 84, which may be composed ofa plurality of digital imaging detectors 85. According to one aspect,these digital detectors comprise either a CMOS, CCD, or photo diodearray.

As a sample body fluid, such as whole blood, flows vertically throughthe test pad 20, red blood cells can be filtered or blocked from theopposite side of the test pad 20, which is generally viewed as beingpreferable so as to enable a more accurate reading of the levels ofanalyte present in the sample. The chemical reagents and dye productsutilized in test pad 20 can be chosen from any number of well knowsubstances. In any event, these chemistries should provide a discernableand readable reaction over an appropriate range of analyte concentrationlevels. In the case where the device is to be utilized to monitor theconcentration of glucose contained in samples which comprise mainlywhole blood, these chemistries should be able to produce reactions whichcan then be detected to indicate a glucose concentration ranging from,for example, 40-500 mg/dL.

According to a preferred aspect, the detector array 84 is formed from aplurality of individual CMOS-type detectors 85. CMOS detectors are lesscostly than other types of digital imaging devices. As described above,due to the time-dependent aspect of the arrangement 80, which mayinclude CMOS detectors 85, various “clock” or time-driven electronicdevices may be incorporated. Data can be taken from the detectors 85 andfed to such devices (directly or from storage) thereby enabling themonitoring and interpretation of the kinetics and other aspects of thereaction between the analyte and the reagent.

By the utilization of an array 84 of individual detectors 85, uniformityand accuracy of the assay is also promoted. For example, readings aretaken and utilized from multiple individual detector elements, orpixels, are less susceptible to variations in uniformity of thematerials of the assay pad, or other localized abnormalities, which canbe accounted for and corrected by the interpretation and manipulation ofthe data generated by the individual pixels 85 of the detector array 84.For example, statistical analyses and associated algorithms may be usedto correct for such localized defects, and therefore improve theaccuracy of the overall reading generated by the device.

FIGS. 9 and 10 represent a scan performed by an arrangement 80 such asthe one depicted in FIGS. 8 a and 8 b. FIG. 9 is a picture of a testspot formed on a commercially-available assay pad. FIG. 10 is a plot ofthe signal generated by an array of detector elements 84 as they arescanned along the dashed line contained in FIG. 9. As illustrated inFIG. 10, the lower voltage readings correspond to the area occupied bythe test spot of FIG. 9 along the dashed line.

FIG. 11 is a schematic illustration of one possible construction for theassay pad 20. The assay pad construction 1100 has a sample applicationside SA as well as an analysis side A. According to one construction,the assay pad 1100 is composed of at least 3 constituent components: ablocking component 1102; a membrane component 1104; and a chemicalreagent component 1106. When the sample to be analyzed is composed atleast in part of whole blood, red blood cells are separated from theplasma, which is then transported to the reagent component 1106 whichincludes enzymatic chemistries selected to produce a chemical reactionwith one or more analytes present in the sample.

The blocking component 1102 may include an agent to filter or pre-filterred blood cells. By way of example, the blocking component 1102 mayinclude zirconium oxide (ZrO₂).

The membrane component 1104 can be formed of any suitable material. Forexample, the membrane be a high light transmitting material, oroptionally can be an opaque or substantially opaque material. Suitablematerials may include styrene and/or nylon. The membrane component 1104can be in woven or non-woven form. According to one aspect, the membraneis in the form of a woven mesh.

As indicated above, the reagent component 1106 is chosen according toits ability to react with the analyte under investigation. Any suitablereagent chemistry can be utilized. Specific examples of suitablematerial include a glucose oxidase (e.g.—from Biocatalysts productG575P), a soybean peroxidase (e.g.—from Organic Technologies, product73930.1 medical diagnostic grade), an amino antipyrine hydrochloride(e.g.—from TCI, product A0257) and an Aniline derivative dye for a“Trinder” reaction (see, e.g.—P. Trinder, “Determination of Glucose inBlood Using Glucose Oxidase with an Alternative Oxygen Acceptor”).

While the various constituent components of the assay pad construction1100 are illustrated in FIG. 11 as distinct layers, it should beunderstood that the present invention is not limited to such aconstruction. For example, the blocking component 1102 and/or thereagent component 1106 may be partially or entirely subsumed andcontained within the membrane component 1104. Thus, it is entirelypossible that a surface “layer” of the blocking component 1102 and/orreagent component 1106 may be present. Alternatively, the blockingcomponent 1102 and/or the reagent component 1106 may be entirelysubsumed, contained or impregnated within the membrane component 1104,such that no distinct blocking component “layer” or reagent component“layer” is present at all.

It should be noted, that not only with respect to the embodimentdepicted in FIG. 11, but as well as with all of the followingalternative test strip constructions according to the present invention(e.g.—FIGS. 12-16), similar alternative constructions to that explicitlydescribed above are comprehended within the scope of the presentinvention. For instance, the constituent components described herein arenot limited to distinct “layers”. Rather, one or more of the constituentcomponents of the test strip constructions described herein may bepartially, or entirely, subsumed, contained or impregnated within otherconstituent components of the test strip constructions and therefore notbe present as distinct “layers”.

With respect to the embodiment depicted in FIG. 11, the blockingcomponent 1102 and/or reagent component 1106 may be applied to themembrane component 1104 in any suitable manner. For example, theblocking component 1102 and/or reagent component 1106 may be coated uponthe membrane 1104. An example of suitable coating techniques includesspin coating.

FIG. 12 illustrates one possible alternative construction 1200 for theassay pad 20. According to one construction, the assay pad construction1200 is composed of at least 4 components: a prefilter and reflectivecomponent 1202, a membrane component 1204, a reagent component 1206, anda mesh component 1208. With the above-described structure, in the casewhere the substance to be analyzed is a sample which is composed atleast in part of whole blood, the red blood cells are separated from theplasma, so that components 1202 and/or 1204 retain the red blood cellswithout lysis. The plasma is then vertically transported to the reagentcomponent 1206 which includes enzymatic chemistries. These substancesmay include any suitable material, which are generally known in the art.Specific examples of suitable materials include a glucose oxidase(e.g.—from Biocatalysts product G575P), a soybean peroxidase (e.g.—fromOrganic Technologies, product 73930.1 medical diagnostic grade), anamino antipyrine hydrochloride (e.g.—from TCI, product A0257) and anAniline derivative dye for a “Trinder” reaction (see, e.g.—P. Trinder,“Determination of Glucose in Blood Using Glucose Oxidase with anAlternative Oxygen Acceptor”).

The component 1204 may comprise any suitable blood-filtering componentor material. Some materials which have been used to separate red bloodcells from plasma and samples of whole blood include glass fibers, meshcloth, unwoven mats, asymmetric membranes, and porous polymers.

Regardless of what type of material is chosen for component 1204, theavoidance of spreading or lateral diffusion, which may occur with suchmaterials as poly (ethersulfone) membranes, is desirable. An exemplarysuitable material is, a hydrophilic poly(vinylidene fluoride) unwovenmembrane. Such membranes are commercially available from the MilliporeCorporation (e.g.—with 0.1 micron openings). Other suitable materialsinclude unwoven membranes comprising a polyamide. Other materials may beincorporated to achieve various performance objectives, such aspoly(acrylic acid) (PAA), hydroxyethyl cellulose, sodium alginate, andgelatin.

The pad 1200 may further include a component 1202, such as a prefilterand/or diffuse reflection component. Thus, the component 1202, whenincluded, serves to improve separation of red blood cells from a samplecontaining whole blood, and/or increase the reflection of incident lightupon the opposite side of the pad when undergoing optical analysis.Suitable materials for use as component 1202 include a zirconium oxide(ZrO₂), optionally combined with a polymer binder material. Thecomponent 1202 can be applied to the membrane, or component 1204, byusing any suitable technique. One such suitable technique is spincoating. Spin coating promotes uniform distribution of the component1202 onto and/or within the membrane component 1204. As previouslyexplained, while components 1202 and 1204 have been illustrated asdistinct layers, the component 1202 may be partially, or entirelycontained within the membrane component 1204, thus effectively combiningthese two components into a single unitary member, rather than theillustrated distinct layers. When, according to the above-describedalternative embodiment, the component 1202 comprises a prefilter anddiffuse reflection material and a polymer binder, the presence of thepolymer binder tends to form at least a thin layer or film over themembrane component 1204. This thin film may have any suitable thickness,for example, the component 1202 may partially permeate the membranecomponent 1204 and leave a thin film having a thickness on the order ofless than 5 micrometers on top of the membrane component 1204.

The component 1206 comprises a reagent which may be formed from anysuitable composition, such as the chemicals described above, and mayoptionally be provided in a binder of poly(acrylic acid),hydroxypropylmethylcellulose (HPMC) or similar polymers that reducelateral spreading of the substrate or sample undergoing analysis.

The mesh component 1208 and the reagent 1206 component may also beintegrated into a single layer or constituent element of the test pad20. For example, reagent material 1206 can be coated onto the meshcomponent 1208. Any suitable coating technique may be utilized. A spincoating technique is one such technique for providing the reagent on themesh component 1208 which allows for precise and relatively thin coatingof the reagent component 1206 to be applied to the mesh component 1208.According to one construction, this “coating” is entirely absorbed andcontained within mesh component 1208. The mesh component 1208 should bepermeable to oxygen in order to promote the reaction of the analyte withthe chemical reagent component 1206. According to one aspect, the meshcomponent 1208 can be formed from a high reflectance woven mesh, such asnylon. Thus, according to one aspect, mesh component 1208 is formed froman open polyamide or nylon mesh material. This nylon mesh materialhaving a reagent incorporated therein is believed to increase thesensitivity of the assay. The open structure of the nylon mesh, inconjunction with the controlled amount of the reagent component material1206 incorporated therein, increases the diffuse reflection of lightincident thereon. This increased diffuse reflection is believed to becaused by the multiple reflections and increased path lengths providedby the open nylon mesh structure. According to one exemplary embodimentshown in FIG. 13, the mesh component 1208 has openings have a dimensionwhich is on the order of 68 microns, and a filament diameter which is onthe order of approximately 50 microns. The region indicated by circle A₁illustrates the absence of reagent material within the mesh, wherein thereagent material has been consumed by chemical reaction with theanalyte. Circle A₂ indicates an area of the mesh in which the reagentmaterial is still disposed thereon.

The cylindrical fibers of the nylon mesh may scatter the light onto theexternal exposed layer or surface thereby introducing multiplereflection and increased path links. The scattering of incident light islargely dependent upon a refractive index of the cylinders which formthe filaments of the mesh. The refractive index of nylon is relativelarge, on the order of 1.53, and this is beneficial. Moreover, theabove-described application of the reagent component 1206 to the meshcomponent 1208 can simplify manufacture.

Another alternative test pad or test strip construction 1400 isillustrated in FIG. 14. According to one aspect, the test padconstruction 1400 includes three basic components: a filter and/ordiffuse reflective component 1402, a chemical reagent component 1404,and a membrane component 1406. As previously discussed, a sample to beanalyzed is applied to the sample application side SA of test pad 1400.When the sample contains, at least in part, whole blood, red blood cellsare separated from the plasma by component 1402 and are transported tothe reagent component 1404, which may be partially or entirelyimpregnated it the membrane component 1406.

The component 1402 may be formed from any suitable construction thatprovides filtration and/or diffuse reflection functions. For example,suitable constructions have been described above. According to onespecific example, the component 1402 may comprise a zirconium oxidematerial combined with a permeable polymer binder material, such asHPMC, that limits lateral diffusion. Another suitable example includes azirconium oxide material combined with a permeable polymer binder suchas vinyl butyral. The zirconium oxide and polymer binder are combined inany suitable proportions, such as 20:80.

The reagent component 1404 includes at least one chemical reagent chosento provide a suitable reaction with the analyte(s) under investigation.Any suitable reagent can be chosen. For example, the reagent maycomprise a glucose oxidase, soy bean peroxidase, amino antipyrinehydrochloride, and/or aniline derivative dyes. The chemical reagent mayoptionally be combined with a binder component. When present, the bindercomponent is preferably formed from a material which reduces thetendency for lateral spreading of the sample within the test pad 1400.Suitable examples binder material examples include HPMC and PAA.

A suitable membrane component 1406 can also be provided. According toone embodiment, the membrane component 1406 can comprise a fibrousunwoven material. One specific example includes a cellulose acetateunwoven fibrous membrane material.

Both the filter/diffuse reflective component 1402, as well as thereagent component 1404 can be applied to the membrane component 1406 byany suitable technique. According to one example, the reagent component1404 is applied to the membrane component 1406 by a coating technique,such as spin coating. Reagent component 1404 may be partially, orentirely impregnated within the membrane component 1406. Thus, a thinfilm or layer of reagent component 1404 may be present on the topsurface of the membrane component 1406 (i.e.—the side closest to thesample application side SA of the test pad 1400). When present, thisthin top layer can be on the order of a few microns in thickness.Alternatively, the reagent component may be entirely subsumed, containedor impregnated within the membrane component 1406, such that no distinctlayer is present on the top surface of the membrane component 1406(i.e.—the surface of membrane 1406 which is closest to the surfaceapplication side SA of the pad 1400).

The filter/diffuse reflective component 1402 can then be appliedsubsequent to application of the reagent component 1404. The component1402 can also be applied by any suitable technique, such as spincoating. According to one specific example, a filter/diffuse reflectivecomponent comprising a zirconium oxide and hydrophobic permeable polymerbinder material is spin coated at approximately 1000 rpm onto themembrane/reagent components 1406/1404. The filter/diffuse reflectivecomponent 1402 may be partially impregnated within the membrane 1406,leaving a thin film layer at the surface application side SA of thecombined membrane and reagent components 1406 and 1404. When present,this thin surface layer can be a few microns in thickness, for example,on the order of less than 5 microns in thickness. Alternatively, thefilter/diffuse reflective component 1402 may be entirely subsumed,contained, or impregnated within the combined reagent and membranecomponents 1404 and 1406.

An additional test pad construction 1500 consistent with the principlesof the present invention is illustrated in FIG. 15. According to oneaspect, the test pad construction 1500 is comprised of at least fourbasic components: a filter/diffuse reflective component 1502, apermeable material component 1504, a reagent component 1506, and amembrane component 1508. The general functionality of the test pad 1500and the functionality of the individual components thereof are similarto that previously described.

The component 1502 may comprise any suitable filter and/or diffusereflective material. For example, the component 1502 may comprise azirconium oxide material with or without a polymer binder. Whenincluded, the polymer binder is preferably a permeable material.Examples of suitable permeable polymer binders include HPMC and anacrylic resin, such as Elvacite®.

The component 1504 is preferably comprised of a suitable permeablematerial which can be hydrophobic. The hydrophobic material can compriseany suitable form. According to one example, the component 1504 maycomprise a film of a hydrophobic polymeric material, such as PAA. Thefilm can be formed by any suitable technique. For example, a film of PAAis formed by a fast evaporating solvent/PAA mixture. According to onespecific example, the mixture may contain 10% by weight (relative to theweight of the solvent) of PAA.

The component 1506 may comprise a suitable reagent material. The reagentmaterial may be combined with a binder. The reagent component may bechosen from any suitable substance or combination of substances, asdescribed above. When present, the binder material comprises a permeablehydrophobic binder material. One suitable example is HPMC.

The membrane component 1508 can be formed from any suitable material.According to one possible construction, the membrane component 1508 isformed from an unwoven fibrous mat. For example, the reagent component1506 can be spin coated upon the membrane component 1508. As discussedabove, the reagent component 1506 may be partially, or entirely,impregnated within the membrane component 1508. Thus, the reagentcomponent 1506 may or may not comprise a thin surface layer formed ontop of the membrane component 1508 (the top side being closest to thesurface application side SA of the test pad 1500).

The hydrophobic material component 1504 can then be applied. Accordingto one possible technique, the hydrophobic material can be formed as aslurry or mixture with a fast evaporating solvent, such as methanol. Themixture is then coated onto the combined membrane and reagent components1508 and 1506. Subsequent to evaporation, a thin film of the hydrophobicmaterial is left on top of the combined reagent/membrane component.

The component 1502 may then be applied to the previously describedcombined components. According to one example, a combination offilter/diffuse reflective material, e.g.—ZrO₂, and a polymer bindermaterial, such as the ones described above, may be combined in the formof a slurry or mixture and then coated upon the previously combinedcomponents. According to one specific example, a slurry containing up to10% by weight of ZrO₂ may be formed and then spin coated onto theprevious combined constituent components 1504, 1506, and 1508. Aspreviously discussed, the component 1502 may be partially or entirelyimpregnated or subsumed within the previously combined components. Thus,the component 1502 may be indistinguishable from the previously combinedcomponents or, may form a thin film or layer on top of the previouslycombined components.

Yet another alternative test pad construction 1600 formed according tothe principles of the present invention is illustrated in FIG. 16. Thetest pad construction 1600 illustrated therein is formed from at leastthree basic constituent components: a filter/diffuse reflectivecomponent 1602, a permeable hydrophobic material component 1604 and acombined reagent/mesh component 1606. The basic functionality of theindividual as well as combined constituent components of the test padconstruction 1600 is similar to that previously discussed.

The filter/diffuse reflective component 1602 can be formed from anysuitable material, and comprise any suitable construction. According toone possible embodiment, the component 1602 comprises a zirconium oxidematerial, which may optionally be combined with a binder material. Whenpresent, the binder material is preferably a permeable hydrophobicbinder material such as an acrylic resin. Such material is beingcommercially available, e.g.—sold as Elvacite®.

Similarly, the permeable hydrophobic material component 1604 can becomprised of any suitable material, and take any suitable form. By wayof example, the permeable hydrophobic material can comprise a film orlayer. According to one specific example, the permeable hydrophobicmaterial may comprise PAA.

The combined reagent/mesh component 1606, as implied is preferably thecombination of two distinct parts or constituents. Namely, a reagentmaterial such as those previously described, as well as a mesh materialconstituent. Preferably, these constituents are combined into a single,integral component 1606. The mesh material can be formed of any suitablematerial and take any suitable form. For example, the mesh material canbe formed from a woven polyamide material, such as a woven nylon mesh.The mesh may have openings of any suitable dimensions, such as either 30microns openings or 41 micron openings.

The above-described constituents can be applied to one another orcombined in any suitable manner.

According to one specific example, the reagent and the mesh componentare combined or integrated by soaking the mesh material in a slurryformed from the reagent material. For example, a slurry or mixture canbe formed which comprises 20% by weight HPMC binder material plus asuitable reagent chemistry. The mesh material is soaked in this liquidslurry. The mesh material is then removed and dried, thereby leaving anintegrated mesh/reagent component 1606.

The hydrophobic component 1604 can be similarly be applied by anysuitable technique. For example, as described above, the hydrophobicmaterial can be applied as a film formed from a fast evaporatingsolvent, like methanol. According to one specific example, a hydrophobicmaterial, such as PAA is combined with a solvent to form a slurry.According to one embodiment, the slurry may comprise 10% by weight ofthe PAA material. The solvent is then applied to the combinedreagent/mesh component 1606. Upon evaporation of the solvent, a thinfilm or layer of the hydrophobic material is left behind, therebyforming the hydrophobic material component 1604.

The filter/diffuse reflective component 1602 may similarly be applied byany suitable technique, such as those previously described. According toone aspect example, a zirconium oxide material is added to a hydrophobicbinder to form a slurry in an evaporative solvent such as toluene.According to this specific example, the slurry contains approximately10% by weight of acrylic resin such as Elvacite®. This slurry is thencoated onto the combined hydrophobic and reagent/mesh components 1604and 1606. Any suitable coating technique can be utilized, such as theaforementioned spin coating technique.

According to one possible construction, the filter/diffuse reflectivecomponent 1602 is provided in the form of a thin layer or film on top ofthe combined hydrophobic material and reagent/mesh component 1604 and1606.

While the present invention has been described by reference to theabove-mentioned embodiments, certain modifications and variations willbe evident to those of ordinary skill in the art. Therefore, the presentinvention is limited only by the scope and spirit of the appendedclaims.

1-58. (canceled)
 59. A device for conducting an assay to determine theconcentration of an analyte in a sample of bodily fluid, the devicecomprising: a skin-penetration member configured to collect the sample;a sample collection chamber configured to receive the sample from theskin-penetration member; an assay pad in communication with at least oneopening of the sample collection chamber, assay pad comprising a reagentadapted to produce a reaction when exposed to the analyte; and at leastone detector disposed relative to the assay pad so as to detect thereaction, wherein the sample collection chamber is configured such thatwhen the sample is received by the sample collection chamber the sampleflows laterally or axially through the chamber, then flows verticallytoward the assay pad.
 60. The device of claim 59 wherein the at leastone detector comprises a sensor, the sensor comprising a CMOS sensor, aCCD sensor, or a photodiode.
 61. The device of claim 59, wherein theanalyte comprises glucose.
 62. The device of claim 59, wherein the atleast one detector comprises a linear array of CMOS sensors.
 63. Thedevice of claim 59, wherein the skin-penetration member comprises amicroneedle.
 64. The device of claim 59, further comprising a lightsource adapted to provide light incident upon the assay pad.
 65. Thedevice of claim 59, further comprising a lens disposed between the atleast one detector and the assay pad.
 66. The device of claim 65,wherein the lens is a refractive lens.
 67. The device of claim 65,wherein the lens is a diffractive lens.